In recent years, as miniaturization of devices, such as a sensor, advances, development of wearable transmission type HMDs (Head-Mounted Displays) called, for example, a smart glass becomes more active. Generally, an information display system using such a transmission type HMD projects or displays information as an information image on a transparent virtual screen (a lens or lenses of glasses, or a glass or plastic material on the front surface of sunglasses or goggles), so that a wearing person (user) can confirm the information while looking at the background. That is, one of the features of the transmission type HMD is to be able to display (superimposing display) an information image while superimposing the information image on the background being an ambient environment.
However, conventional transmission type HMDs have a problem that the information image displayed on a virtual screen becomes an obstacle for a view field of a wearing person (user) depending on the position of a sight line of the user, which is a problem coming from the feature to perform the superimposing display. Some techniques for avoiding this problem have been proposed.
As an example of a technique to project and/or display an information image on a transparent virtual screen, which is not a technique relating to a wearable transmission type HMD, Japanese Examined Patent Application Publication (JP-B) No. 04698002 discloses a display apparatus for use in a vehicle. The display apparatus is configured to detect a sight-line direction of a driver and to judge whether information to be recognized by the driver is information of a predetermined kind or information other than that. The display apparatus is further configured to, when having acquired the information of the predetermined kind (such as alarm information for the driver and vehicle control information indicating that vehicle control is being performed), set the display position of an image of the information to be displayed by a display unit, on the windscreen and on or around the axis of the sight-line direction of the driver, on the basis of the judged kind of the information and the sight-line direction of the driver. The display apparatus is further configured to, when having acquired the other kind of information (such as information relating to information provision other than the alarm information and the vehicle control information), set the display position of the image of the information at a predetermined base display position on the windscreen.
However, in the above conventional technique, the display position of an information image on the virtual screen is set at either one of the vicinity of the position of a sight line and the base display position in accordance with the kind of the information, and the base display position is fixed. The reason why such control is performed is that the above conventional technique conceives the application for HUD (Head-Up Display) in a vehicle and includes implicitly a precondition that the base display position does not become an obstacle for a view field of a driver. Accordingly, for example, in the case where a user wants to refer to the background located beyond the information image displayed at the base display position on the virtual screen, the display of the information image cannot be prevented from becoming an obstacle for the view field of the user.
For such a problem, a considerable method is to shift an information image overlapping with the position of a sight line on the virtual screen. However, if the information image overlapping with the position of a sight line is merely shifted on the virtual screen, it may bring a result contrary to a user's intention.
For example, when a user gazes on the background (peripheral environment) located farther than an information image on the virtual screen, the displayed information image may become an obstacle for the view field of the user. However, when a user gazes at an information image on the virtual screen, the shift of the display position of the information image makes a user's confirmation of the information image difficult. That is, it is necessary to judge whether an information image on the virtual screen is to be shifted, on the basis of a gaze position of the user. Therefore, with the control in which an information image is shifted uniformly without making such a judgment, a transmission type HMD hardly displays an information image appropriately while securing a view field of a user properly.
Further, when an image of information having no (or low) relevance to the background is being displayed, it is considered that the shift of the display position of the information image causes no problem. However, when an image of information intended to be superimposed on the background is being displayed, the shift of the display position of the information image can impair the value of the information. That is, it is necessary to judge whether or not an image of information displayed on the virtual screen is to be shifted, depending on the kind of information. Therefore, with the control in which an information image is shifted uniformly without making such a judgment, a transmission type HMD hardly displays an information image appropriately while securing a view field of a user properly. The present invention seeks to solve the problem.